(704d) Development of a Novel Process That Converts Waste Plastic to Propylene

Propylene is a key chemical compound in the petrochemical industry, with current global production reaching 150.3 million metric tons per year. Propylene is primarily used in the production of polypropylene, which is the world's second-largest plastic resin based on production volume, after polyethylene. By 2026, it is forecast that polypropylene production will amount to 88 million metric tons. Despite accounting for 16% of plastics production, polypropylene has a notably low recovery rate of only 1%, with the majority ending up in landfills or the environment. Furthermore, the current industrial production of propylene occurs via propane dehydrogenation, which suffers from unfavorable thermodynamics where the equilibrium favors the reactants and consumes a lot of energy. These factors provide the motivation to consider the development of processes that convert waste plastics, notably polypropylene, to propylene in an economical manner.

In this project, a novel process is developed that utilizes waste plastic to produce propylene. Waste polypropylene is reacted in a microwave reactor to produce a mixture of olefins. Preliminary experimental results indicate that it is possible to get 48% selectivity in the production of propylene. Furthermore, the microwave process requires significantly less energy compared to the conventional thermal process as conversion to olefins occurs at a bulk temperature of 400 ^oC, whereas thermal heating requires a temperature of over 600 ^oC. This experimental data is utilized to develop a conceptual flowsheet in the ASPENPlus environment. A separation scheme based on a train of distillation columns is developed to produce industrial quantities of polymer-grade propylene. Heat integration tools are utilized to reduce the hot and cold utilities used in this process. This novel design is compared with the conventional process of making propylene via propane dehydrogenation. A technoeconomic analysis is conducted to demonstrate the economic feasibility of this process.